W poszukiwaniu filogenezy ssaków mezozoicznych

Zhe-Xi Luo, Zofia Kielan-Jaworowska, and Richard L. Cifelli

Acta Palaeontologica Polonica 47 (1), 2002: 1-78

We propose a phylogeny of all major groups of Mesozoic mammals based on
phylogenetic analyses of 46 taxa and 275 osteological and dental
characters, using parsimony methods (Swofford 2000). Mammalia sensu lato (Mammaliaformes of some authors) are monophyletic. Within mammals, Sinoconodon is the most primitive taxon. Sinoconodon, morganucodontids, docodonts, and Hadrocodium
lie outside the mammalian crown group (crown therians +Monotremata) and
are, successively, more closely related to the crown group. Within the
mammalian crown group, we recognize a fundamental division into
australosphenidan (Gondwana) and boreosphenidan (Laurasia) clades,
possibly with vicariant geographic distributions during the Jurassic and
Early Cretaceous. We provide additional derived characters supporting
these two ancient clades, and we present two evolutionary hypotheses as
to how the molars of early monotremes could have evolved. We consider
two alternative placements of allotherians (haramiyids
+multituberculates). The first, supported by strict consensus of most
parsimonious trees, suggests that multituberculates (but not other
alllotherians) are closely related to a clade including spalacotheriids
+crown therians (Trechnotheria as redefined herein). Alternatively,
allotherians can be placed outside the mammalian crown group by a
constrained search that reflects the traditional emphasis on the
uniqueness of the multituberculate dentition. Given our dataset, these
alternative topologies differ in tree-length by only ~0.6% of the total
tree length; statistical tests show that these positions do not differ
significantly from one another. Similarly, there exist two alternative
positions of eutriconodonts among Mesozoic mammals, contingent on the
placement of other major mammalian clades. Of these, we tentatively
favor recognition of a monophyletic Eutriconodonta, nested within the
mammalian crown group. We suggest that the "obtuse-angle symmetrodonts"
are paraphyletic, and that they lack reliable and unambiguous
synapomorphies.